1. Field of the Invention
The present invention relates to a coder/decoder (“codec”), and, more particularly, to providing and operating an audio codec with a gain controller utilizing a modified R2R ladder network for controlling volume during playback of audio signals and for controlling gain of audio signals during a capture operation.
2. Description of Related Art
A (coder/decoder) (“codec”) is considered to be any technology that encodes and decodes data. The encoding and decoding of data is useful and important to the processing of data in analog, digital, and mixed signal systems. Codecs may be implemented in software, hardware, or a combination of both software and hardware. Also, an exemplary type of audio codec is the audio codec (“AC”) '97, which Intel Corporation has published in various revisions of the specification entitled Audio Codec '97 (“AC '97) (e.g., revision 2.2 in September 2000; revision 2.1 in May 22, 1998; revision 2.0 in Sep. 29, 1997; revision 1.03 in Sep. 15, 1996). The AC '97 specification and its various revisions are hereby incorporated by reference.
The AC '97 specification, revision 1.03 comprehensively defines a serial codec device that is designed to be utilized in systems in which audio signal processing and audio analog-to-digital (A/D) and digital-to-analog (D/A) conversions are performed in separate devices. The AC '97 specification, revision 2.0 is a follow-up revision to revision 1.03 and further defines the interface for a combined audio/telephony codec. Revision 2.0 also includes definitions for modem sample rate control, tagged data exchange using different sampling rates, general purpose input/output definitions, and extended AC-link definitions for multiple devices and power management event handling. Revision 2.1 updates revisions 1.03 and 2.0 by including some electrical and power management updates. Revision 2.2 provides further updates to revision 2.1 by adding optional S/PDIF support, standardized slot re-mapping, and updated electrical specification for better riser support.
Codecs typically require modules for input volume control and mixing of several analog input sources for a playback operation of an audio device. An input volume control is implemented with an operational amplifier (“op amp”) and a resistor string. A codec may typically have ten to fourteen input volume control modules connected to the output mixer. Each input volume control module receives a gain control bit that is decoded to switch on a respective switch in the output mixer to set the appropriate gain. Each op amp in the input volume control module requires a calibration digital-to-analog converter (DAC) and respective logic for canceling offsets to minimize noise, such as pops and clicks, in the output signal. A gain control module similar to the input volume control module is utilized to mix analog input sources during the capture operation of the audio device. The gain control module also requires a calibration DAC and respective logic for canceling offsets that may occur during the mix and capture of the signals to minimize noise. However, op amps and calibration circuitry may consume a significant amount of die area. Therefore, a desire and need exist to provide input volume control modules or gain control modules that cancel offsets and minimize noise and that still do not consume a significant amount of die area.
The present invention recognizes the desire and need for providing an input volume controller or a gain controller that cancels offsets and reduces noise and that still consumes a low amount of die area. More specifically, the present invention provides an input volume controller or a gain controller that mixes and/or selects one of multiple analog sources with independent gain control using a modified R2R ladder scheme. The present invention overcomes the problems and disadvantages that have been encountered with the prior art.